What are the classifications of LED chips?

The core of LED is semiconductor chip. One end of the chip is attached to the bracket, one end is the negative electrode, and the other end is connected to the positive electrode of the power supply, so that the whole chip is encapsulated by epoxy resin. LED chip, also known as LED light-emitting chip, is the core component of LED lamp, namely pn junction. So what are the classifications of LED chips? MB chip, GB chip, TS chip and AS chip are the most common. Let's study related knowledge with Bian Xiao. What are the classifications of LED chips?

MB chip

Definition: MB Chip _ Metal Bonding Chip _ This chip belongs to UEC patent product.

GB chip

Definition: GB chip _ adhesive chip _ This chip belongs to UEC patent product.

TS chip

Definition: TS Chip _transparentstructure Chip _ This chip belongs to HP's patented product.

As a chip

Definition: As a chip _ Absorbable structural chip _ After nearly 40 years of development efforts _ R&D _ production _ sales of this type of chip in Taiwan Province LED photoelectric industry are in a mature stage _ R&D levels of major companies in this field are basically at the same level _ The gap is not big. The mainland chip manufacturing industry started late, and there is still a certain gap between its brightness and reliability and Taiwan Province's industry. What we are talking about here is as the core. Chip _ refers to the chip of UEC _ for example: 7 12sol-VR, 709sol-VR, 7 12sym-VR, 709sym-VR, etc.

Types of LED chips

1, LPE: liquid phase epitaxy GaP/GaP.

2.VPE: vapor Xiang Lei crystal method GaAsP/GaAs.

3.MOVPE: metallurgical vapor phase epitaxy (organic metal gas Xiang Lei crystal method) AlGaInP, GaN.

4. SH: gaalas/gaassinglexedostructure (simplex structure) GaAlAs/GaAs.

5. DH: gaalas/gaasdoublehetrostructure, (double-shaped structure) GaAlAs/GaAs.

6.DDH: GaAlAs/GaAlAs double heterostructure (double heterostructure).

Manufacturing technology of LED chip

1, LED chip detection

Microscopic examination: whether there is mechanical damage on the surface of the material, whether the chip size and electrode size of the pockmarked lock meet the technological requirements, and whether the electrode pattern is complete.

2.LED expansion

Because the LED chips are still closely arranged after dicing, the spacing is very small (about 0. 1mm), which is not conducive to the subsequent process operation. The film bonded to the chip is expanded by the film stretching machine, so that the pitch of LED chips is stretched to about 0.6 mm Manual expansion is also possible, but it is easy to cause bad problems such as chip loss and waste.

3, LED dispensing

Apply silver glue or insulating glue to the corresponding position of LED bracket. For GaAs and SiC conductive substrates, red, yellow and yellow-green chips with back electrodes are made of silver paste. For blue and green LED chips with sapphire insulating substrate, insulating glue is used to fix the chips.

The process difficulty lies in the control of dispensing amount, and the height and location of colloid have detailed process requirements. Because there are strict requirements for the storage and use of silver glue and insulating glue, the proofing, stirring and use time of silver glue are all matters that must be paid attention to in the process.

4. Preparation of LED glue

Contrary to dispensing, glue making is to apply silver glue to the electrode on the back of LED with a glue making machine, and then install the LED coated with silver glue on the LED bracket. The efficiency of dispensing is much higher than dispensing, but not all products are suitable for dispensing.

5, LED manual puncture

Put the expanded LED chips (with or without glue) on the fixture of the stabbing table, put the LED bracket under the fixture, and stab the LED chips to the corresponding positions one by one with a needle under the microscope. Compared with automatic mounting, manual punching has an advantage that it is convenient to replace different chips at any time, and it is suitable for products that need to install multiple chips.

6. Automatic LED installation

In fact, automatic mounting is a combination of two steps: gluing (gluing) and chip mounting. First, apply silver glue (insulating glue) on the LED bracket, then suck up and move the LED chip with a vacuum nozzle, and then put it in the corresponding bracket position. In the process of automatic mounting, it is mainly necessary to be familiar with the equipment operation programming, and at the same time, to adjust the gluing and installation accuracy of the equipment. In the selection of suction nozzle, try to use bakelite suction nozzle to prevent damage to the surface of LED chip, especially for blue-green chip. Because the steel nozzle will scratch the current diffusion layer on the chip surface.

7, LED sintering

The purpose of sintering is to solidify the silver paste, and the sintering needs to monitor the temperature to prevent batch defects. The sintering temperature of silver paste is generally controlled at 65438 050℃ and the sintering time is 2 hours. It can be adjusted to 170℃ and 1 hour according to the actual situation. Insulation glue is generally 150℃ 1 hour.

The silver glue sintering furnace must be opened every 2 hours (or 1 hour) according to the process requirements to replace the sintered products, and it is not allowed to be opened at will. The sintering furnace shall not be used for other purposes to prevent pollution.

8.LED pressure welding

The purpose of pressure welding is to lead the electrode to the LED chip and complete the connection of the internal and external leads of the product.

There are two bonding processes for LED: gold wire ball bonding and aluminum wire bonding. The process of aluminum wire bonding is to press the first point on the LED chip electrode, then pull the aluminum wire onto the corresponding bracket, and press the second point to pull the aluminum wire off. The gold wire ball welding process is to burn a ball first and then press the first point, and other processes are similar.

Bonding is a key link in LED packaging process, and the main process to be monitored is the arch wire shape, solder joint shape and tension of bonding gold wire (aluminum wire).

9. LED sealant

There are three kinds of LED packaging: glue, potting and plastic packaging. Basically, the difficulties in process control are bubbles, lack of materials and black spots. The design is mainly about the selection of materials, and the combination of epoxy and bracket is selected. (General LED can't pass the air tightness test)

LED dispensing top LED and side LED are suitable for dispensing packaging. Manual dispensing packaging requires a high level of operation (especially white LED), and the main difficulty is to control the amount of dispensing, because epoxy will thicken during use. The dispensing of white LED still has the problem of color difference caused by phosphor precipitation.

LED potting lamp -LED potting. The process of potting is to inject liquid epoxy resin into the LED molding cavity, then insert the pressure welded LED bracket, put it in the oven to cure the epoxy resin, and then take the LED out of the molding cavity for molding.

LED molding and packaging Put the welded LED bracket into the mold, close the upper and lower molds with a hydraulic press and vacuum, put the solid epoxy resin into the rubber channel of the mold with a hydraulic ejector pin, heat it at the entrance of the rubber channel, and the epoxy resin enters each LED molding groove along the rubber channel for curing.

10, LED curing and post-curing

Curing refers to the curing of encapsulated epoxy resin. Generally, the curing conditions of epoxy are 135℃ and 1 hour. Molding and packaging are generally carried out at 150℃ for 4 minutes. Post-curing is to completely cure epoxy resin and thermally age LED. Post curing is very important to improve the bonding strength between epoxy resin and PCB. The general condition is 120℃ for 4 hours.

1 1, LED rib cutting and slicing

Because the LEDs are connected together (not single) in production, the LEDs in the lamp package adopt the method of rib cutting to cut off the ribs of the LED bracket. SMD-LED is on PCB, and it needs dicing machine to complete the separation.

12, LED test

Test the photoelectric parameters of LED, check the overall dimensions, and classify LED products according to customer requirements.